This invention relates generally to controllers for compressors and more particularly to controllers which are applied to control the operation of internal combustion engine prime driver driven compressors.
Electronic controllers have been applied to a great variety of circumstances including controlling the angular velocity of compressors which are often used in the process plant industries. The compressors used in industrial applications are typically electrically powered which operate at a constant angular velocity. However, in locations where it is difficult or impractical to provide an external electric source to power the prime driver of the compressor (such as in portable compressor applications), it is highly desirable to have an internal combustion engine driven compressor. While an electrically driven compressor must operate at constant speed, the angular velocity of internal combustion engine prime drivers, by comparison, can be varied to better accommodate changes in ambient conditions, setpoint pressure and other factors. Control of the angular velocity of the internal combustion engine prime drivers is therefore much more complex than with the electrically powered prime drivers (or other constant speed prime drivers).
Previously, electronic controllers have been applied to control the angular velocity of internal combustion engine prime driver and compressor combinations which are coupled to also drive an electric generator. Since the generator requires a substantially constant angular velocity for proper operation regardless of operating conditions, to maintain a constant frequency, the function of the controller for these internal combustion engine prime driver --centrifugal compressor--generator combinations is to produce a constant angular velocity under all conditions. In the present invention, the angular velocity is maintained at a target value which varies in response to changes in ambient conditions and loading conditions.
This variation of setting of angular velocity for varying conditions permits the compressor to be run at its most efficient state depending upon the specific loading conditions. In the prior internal combustion engine driven centrifugal compressor-generator combinations, it was often necessary to use considerably more energy than necessary by running the compressor at higher angular velocities than necessary (in cold weather), or, in hot weather, to accept a lower than desired discharge pressure because the speed was too low.
To produce a truly energy efficient internal combustion engine prime driver--compressor combination capable of maintaining discharge pressure over a wide ambient range, it is important to ensure that the controller has the capability of being programmed to be able to drive the internal combustion engine prime driver at its most efficient angular velocity based upon the present operating mode. It is also important to ensure that the angular velocity of the prime driver remains within close limits to that which the controller is setting it at.
The foregoing illustrates limitations known to exist in present controllers for centrifugal compressors. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.